This is a subject that doesn't even need to be mentioned. Either regional or global servers, your reason for a curtain one shouldn't be based on player but rather on connection and accessibility. If I was surrounded by nothing but German or French or Japanese players but I don't have lag with super great connection then I'd still be happy.
Better than being flamed by a fellow english speaker for crappy connection- they can go play with their friends with their language.

IMO, connectivity over culture.